Concentrations of heat trapping carbon dioxide in the atmosphere reached a record global average in March, underscoring the crucial importance of reaching an effective universal climate change agreement in Paris at the end of the year.

According to the US National Oceanic and Atmospheric Administration (NOAA), monthly global average concentrations of the gas surpassed 400 parts per million in March 2015 for the first time since the administration began tracking carbon dioxide in the atmosphere. The current concentrations are unprecedented in millions of years.

The US agency says that the rapid rise is mainly attributable to humans burning fossil fuels. Before the industrial revolution began in around 1850, the global concentration stood at 280 parts per million CO2. Half of the current rise occurred since 1980.

These numbers underline the urgency of nations delivering a decisive new universal agreement in Paris in December – one that marks a serious and significant departure from the past.

The agreement and the decisions surrounding it needs to be a long term development plan providing the policies, pathways and finance for triggering a peaking of global emissions in 10 years’ time followed by a deep, decarbonisation of the global economy by the second half of the century - a development plan that crucially also supports the growth as well as the climate ambitions of developing countries.

The 400 parts per million CO2 threshold was already passed at NOAA’s Mauna Loa Observatory in 2013. But this is the first time that the global average crossed the symbolic milestone.

The March figures have only now become available because it takes time for samples to be collected from around the world and analyzed in the NOAA’s laboratory.